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NDTV
3 days ago
- Science
- NDTV
Summer Solstice 2025: When Is The Longest Day Of Year & What Does It Mean?
As summer approaches, the Northern Hemisphere anticipates the Summer Solstice 2025, marking the longest day of the year. This astronomical event occurs when the Earth's axial tilt is most inclined towards the Sun, resulting in the greatest number of daylight hours and the shortest night. When is the Summer Solstice 2025? The Summer Solstice 2025 will take place on Friday, June 20, 2025, at 10:42 PM EDT (0242 GMT on June 21). The exact moment signifies the beginning of summer and the peak of daylight for the Northern Hemisphere. Why Does the Summer Solstice Occur? The summer solstice occurs because Earth's North Pole is tilted closest to the Sun, causing the Sun to reach its highest point in the sky. This alignment results in extended daylight hours, with early sunrises and late sunsets for regions in the Northern Hemisphere. What Does "Solstice" Mean? The term "solstice," derived from the Latin "solstitium" (meaning "sun stands still"), refers to the point when the Sun's apparent motion in the sky pauses before changing direction. Historical Significance of the Summer Solstice The solstice traditionally symbolises the start of summer and has captivated civilisations for millennia. Ancient Greeks like Eratosthenes used the solstice to accurately measure Earth's size. Structures like Stonehenge and Machu Picchu were strategically built to align with the sun during solstices, and in Egypt, the Great Pyramids and Sphinx align with the solstice sunset, demonstrating ancient peoples' deep understanding of the Sun's movements. Earth's Tilt and Its Impact Due to Earth's tilted axis of approximately 23.5 degrees, the Northern Hemisphere receives sunlight at its most direct angle during the solstice, while the Southern Hemisphere enters winter, experiencing its shortest day and longest night. At the solstice's precise moment, the Sun is directly over the Tropic of Cancer, an imaginary line 23.5 degrees north of the equator, marking the beginning of the Sun's southward journey.
Leaders
01-05-2025
- Science
- Leaders
Round vs. Flat: Defying Misconceptions on the Earth's Shape
By: Dr. Mohamed Farag Recently, a controversial question has gone viral across social media platforms: Is the Earth round or flat? Despite the overwhelming evidence and numerous devices proving the Earth is a sphere, including space missions and satellites, some groups claim that the Earth is flat and encircled by an ice wall. Those groups call themselves 'The Flat Earth Society.' Round or Flat? More than 2,200 years ago, Eratosthenes, a Greek astronomer, geographer, mathematician, and poet, proved the Earth's spherical nature. So did Al-Biruni, a Muslim astronomer, mathematician, historian, and geographer. Using the tools available at the time, both scholars calculated the circumference of the Earth with remarkable precision. A depiction of flat Earth Another compelling piece of evidence lies in the shape of other celestial bodies. If you looked through a telescope on a clear night, you would see Jupiter and Saturn appearing as spheres. The Earth is no different. The Age of Earth Scientifically speaking, the age of Earth is estimated to be about 4.5 billion years. Scientists calculated it through geological studies and radiometric dating (the analysis of radioactive elements found in old rocks and minerals). Atoms in radioactive elements decay into lighter elements with lower atomic mass. Each radioactive element needs a certain amount of time for half of its atoms to decay. This is called 'half-life.' By measuring the ratio of the decay products to the ratio of the original element, we can determine how long that sample has been in this location. This method is used to calculate the age of the remains of living organisms and other substances. How the Earth Formed Initially, the universe was void, then it pulsed with matter and energy in what is known as the 'Big Bang.' Matter dispersed across the cosmos, eventually forming hydrogen atoms after a certain period. Following this, hydrogen accumulated in nebulae. Hydrogen nuclei began to fuse in stars, creating radiant stars pulsing with energy. After the consumption of hydrogen in some of those stars, they evolved into red giants or supergiants, depending on their mass. Some of those stars explode, scattering atoms heavier than hydrogen into space. Atoms heavier than iron are formed in neutron stars. Earth Dust particles accumulate in a specific location, forming either a planet or a moon that orbits a planet. Given that gravity operates in all directions, these planets or celestial bodies take a spherical shape. These theories form the basis for the study of the observable universe. They are substantiated by mathematical models and observations. Since the Earth is no different from these planets and stars, it is consequently spherical. Real-world Evidence When you lie down on a beach by the sea or ocean, you will notice ships disappear hull down over the horizon, with the upper parts vanishing last. This is because the Earth's curvature blocks the line of sight to the lower part of the ship. Furthermore, there are plenty of phenomena that confirm that the Earth is a sphere, such as lunar and solar eclipses during which we can simply observe the Earth's shadow on the Moon, as well as the Moon blocking sunlight. Moreover, the change of star positions with the change of geographical location provides another compelling piece of evidence. Similarly, the star constellations visible in the Northern Hemisphere are different from those seen in the Southern Hemisphere. About the author: Dr. Mohamed Farag is an associate professor of physics at Al-Azhar University. Short link : Post Views: 1
